Until now, solar cell modules that directly convert sunlight into electric energy have been widely used in view of effective use of resources and prevention of environmental pollution. Further development of solar cell modules is in progress for improved power generation efficiency, improved weather resistance, and reduced production cost.
A solar cell module is generally produced by laminating a front side transparent protecting member 11 such as a glass substrate, a front side sealing film 13A, solar cells 14 such as silicon crystal photovoltaic elements, a backside sealing film 13B and a backside protecting member (back cover) 12 in this order, as shown in FIG. 1, removing air under vacuum, and heating and pressurizing the stack to cure the front side sealing film 13A and the backside sealing film 13B through crosslinking, thereby adhering and integrating them.
In the solar cell module, a plurality of solar cells 14 mutually connected are used in order to obtain a large amount of electric power. To ensure insulation properties of the solar cells 14, the solar cells are sealed with the sealing films 13A and 13B which have insulation properties.
Meanwhile, development of thin-film solar cell modules prepared using thin-film solar cells such as a thin-film silicon solar cell, a thin-film amorphous silicon solar cell and a copper indium selenide (CIS) solar cell has been promoted. The thin-film solar cell module is produced by forming a photovoltaic element layer such as a semiconductor layer on a surface of a transparent substrate such as a glass substrate or a polyimide substrate by e.g., a chemical vapor deposition method; laminating a sealing film on the photovoltaic element layer; and allowing them to adhere into one body.
Recently, a solar cell sealing material, which is a composition comprising an ethylene-α-olefin copolymer polymerized by using a metallocene catalyst (hereinafter referred to also as m-LLDPE), has been developed (Patent Document 1). Patent Document 1 teaches that a sealing material formed from a composition comprising m-LLDPE and having predetermined physical properties is crosslinked in a relatively short time by an organic peroxide, which provides the sealing material with sufficient adhesivity. This can be expected to enable solar cell modules to attain not only lower production cost but excellent transparency, flexibility, and weather resistance as well as a stable conversion efficiency for a long time.